1. Field of the Invention
The subject of the present invention is a vehicle light device comprising a light guide layer. One preferred application of the invention is the field of automotive equipment for producing light flux used to signal the presence of the vehicle and/or to illuminate part of the surroundings of the vehicle.
Thus, the vehicle light device according to the invention may be:                a motor vehicle lighting device in the strict sense, also referred to as a road lighting device; for example a headlamp, also referred to as a headlight,        a signaling device, such as a turn signal, a stop light, an urban driving light, a nighttime position light or daytime position light (also referred to as a daytime running light or DRL),        a vehicle interior lighting device, such as a roof light or a wall light.        
2. Description of the Related Art
It is common practice to group several lighting and/or signaling functions together into a single housing so as to simplify the electric wiring of these various functions in a motor vehicle.
Moreover, the shape of lighting and/or signaling lights plays an important part in the search for a novel style and look that will allow the motor vehicle to be recognized from afar.
In order to achieve these objectives, it is known practice for the vehicle to be fitted with light guides, also known as layers to guide rays of light.
When looking at a mass or volume light guide, the light inside the guide emerges in accordance with the Snell-Descartes law, according to the value of its angles of reflection and the refractive indices of the various media.
As illustrated in FIG. 1, a light guide 1 is illuminated with rays of light 2.
The light may be reflected or refracted at the boundary between two different media according to the value of the refractive indices n and n′ thereof. According to the Snell-Descartes law, the beam of light changes direction as it passes from one medium to the other.
When, for a ray of light 2, the angle θ between the ray of light and the normal to the surface between the medium of index n and the medium of index n′ exceeds a limit angle θlim, the ray 2 is totally internally reflected within the initial medium n (FIG. 1), with a loss of energy.
As illustrated in FIG. 2, when the angle θ is below the limit angle θlim, the ray 2 is partially refracted in the external medium of index n′, the other part being reflected within the medium of index n.
This principle works perfectly well when the exterior surfaces of the surface or volume light guide 1 are perfectly uniform and polished. Any degradation to one of these surfaces, for example to a zone 3 through a treatment of the graining, striation type etc., causes the light to exit by refraction at the interior surface of the guide (FIG. 3), the output dropping rapidly because there is a loss of energy according to the physical laws of wave guides.
In order to create decorations, all that is required is to define a particular optical pattern, for example using a treatment described hereinabove and illustrated in FIG. 3, so that the optical pattern is visible to an external observer (FIG. 4). Thus, the zone 3 constitutes a zone of optical decoupling allowing the rays of light 2 to be deflected and thus refracted toward the external medium in order to exit the guide 1 and spread in a direction of illumination.
However, to an external observer, the light guide 1 behaves on its lower faces like a mirror, thus generating reflections and ghosting inside the guide 1, detracting from the correct appreciation of the decorative optical patterns. This is in addition to the refracted beams which likewise exit the light guide 1 (FIG. 5).